The first Advisory Opinion on climate change of the International Court of Justice (ICJ) marks a turning point in international legal discourse. The unanimous Opinion, delivered on July 23, 2025, follows a wave of legal developments confirming that States have binding obligations to prevent climate harm. These developments include the 2024 ITLOS Advisory Opinion, which affirmed the duty of States to protect the marine environment from climate impacts, and the Inter-American Court’s Advisory Opinion OC-32/25, which recognized the autonomous right to a stable climate, recognized the jus cogens  obligation not to cuase irreversible damage to the climate and the environment, and reinforced duties of prevention, regulation, and reparation.

This jurisprudential shift builds upon normative resolutions such as the 2021 Human Rights Council resolution and the 2022 UN General Assembly declaration (A/RES/76/300) recognizing the right to a clean, healthy, and sustainable environment. However, no global judicial body has unified these standards in a single, authoritative legal pronouncement.

The ICJ has now confirmed that states’ climate obligations are not merely political or aspirational—they form part of binding international law. These obligations encompass emission reductions and private actors’ regulation, including corporations (para. 428). The Court’s reasoning opens the door to new forms of domestic and international litigation and invites a reassessment of regulatory frameworks such as the EU’s Corporate Sustainability Due Diligence Directive (CSDDD).

In the words of Prof Jorge Viñuales, one of the key architects of the request to the Court and counsel to Vanuatu, the Opinion is “remarkable in its scope,” with the potential to reshape climate accountability frameworks worldwide.

Customary Law, Due Diligence, and Omission Attribution

One of the Court’s most far-reaching contributions is the affirmation that customary international law imposes a binding duty on States to prevent significant harm to the environment, including the climate system (paragraphs 132-139). This obligation is not limited to cases of transboundary harm but extends to global environmental concerns, including climate change and the climate system (para. 135). States must act with due diligence, a standard that the Court described as “stringent” considering the indisputable character of climate risk (para. 138). Due diligence requires the adoption of appropriate rules and their effective implementation and enforcement (para. 138), and, as the Court stresses, regarding climate change, “a heightened degree of vigilance and prevention is required” (para. 138).

In the context of climate change, due diligence requires regulatory mitigation mechanisms designed to achieve “deep, rapid, and sustained reductions of GHG emissions” (para. 282). These measures must reflect scientific evidence, relevant norms (including technical standards and COP decisions), and the principle of common but differentiated responsibilities (paragraphs 284-287).

Failure to take such measures may render the State internationally responsible for an omission, even when the emissions originate from private actors (paragraphs 428–429). The Court clarifies that in such cases, the conduct of the private entity should not be attributed to the State; rather, the attribution arises from the State’s failure to regulate (para. 428).

Corporate Conduct under Scrutiny

The ICJ confirms that state obligations under international law include the duty to regulate non-state actors whose activities contribute to climate harm (para. 428). Omissions in enforcing such regulations may constitute an internationally wrongful act attributable to the State (para. 429). The Court further affirms that fossil fuel licensing, subsidy provision, and regulatory inaction can cause such responsibility (para. 427).

In addtion to that, the Court considers that “the full enjoyment of human rights cannot be ensured without the protection of the climate system and other parts of the environment. In order to guarantee the effective enjoyment of human rights, States must take measures to protect the climate system and other parts of the environment. These measures may include, inter alia, taking mitigation and adaptation measures, with due account given to the protection of human rights, the adoption of standards and legislation, and the regulation of the activities of private actors. Under international human rights law, States are required to take necessary measures in this regard.” (para. 403).

This logic is directly relevant to business and human rights frameworks, where private sector emissions—and the failure to plan for their reduction—must now be seen in light of the State’s duty to act under relevant interlinked obligations in the fields of international human rights law, international environmenatl law and climate change law (para. 404).

Warning to the European Union

The Opinion casts a critical light on the recent weakening of the Corporate Sustainability Due Diligence Directive (CSDDD). While the text in force includes a general requirement for companies to adopt climate transition plans, the current text under discusión as result of the “Ominibus” package restricts this obligation to a limited group of companies under the CSRD.

This raises clear concerns under the ICJ framework. According to the Court, the duty to prevent climate harm applies to all States, including those not party to climate treaties, and requires them to act with all means available to them (para. 409). A state that allows high-emitting corporations to operate without mandatory climate transition plans or corporate due diligence in line with current science may fail to meet its customary obligation to prevent environmental harm (paragraphs 132-139), and, as consequence, commit an internationally wrongfull act.

Equity, Ambition, and Structure of Climate Duties

The ICJ further strengthens the legal character of equity-based principles. It affirms that the principle of common but differentiated responsibilities guides the interpretation of international environmental law (para. 151), and intergenerational equity has normative value in shaping how duties are applied (para. 157).

Most importantly, the Court finds that the Nationally Determined Contributions (NDCs) of the Paris Agreement are not wholly discretionary. While the Paris framework allows for national tailoring, the Court affirms that the standard of due diligence in preparing and implementing NDCs is stringent (paragraphs 165–166). To fulfill their NDCs, states must pursue domestic mitigation measures, and these must reflect their highest possible ambition (para. 166).

The obligation is one of conduct, not result—but compliance requires demonstrable efforts, including the regulation of corporate activities (para. 168).

Toward Enforcement: Loss and Aamage, Attribution, and Legal Remedies

The Court expressly recognizes that loss and damage attributable to climate change may give rise to reparations under the general rules of State responsibility. Where restitution is not feasible, compensation—including financial forms—may be warranted to redress the consequences of internationally wrongful conduct (paras. 195–196). Importantly, the Court affirms that any injured State may invoke the responsibility of another State whose conduct contributed to the harm, even in situations involving cumulative or shared causation (para. 193).

In this context, the Court addresses a long-standing challenge in climate litigation: the diffuse nature of causation. The multiplicity of responsible actors, it holds, does not preclude legal attribution. On the contrary, the Opinion highlights the growing availability of scientific methodologies capable of quantifying the relative contribution of specific activities or omissions to global emissions (para. 194). Such tools—ranging from climate attribution science to emission tracing techniques—are deemed legally relevant in assessing responsibility within a complex, multicausal framework.

This reasoning carries significant implications for the evolving field of climate justice and its intersection with business and human rights. Notably, the Court makes clear that a State may incur international responsibility if it subsidizes fossil fuel production or fails to regulate corporate polluters, where such conduct contributes to identifiable harm—even if the harm results from the combined actions of multiple actors (para. 430). By explicitly linking regulatory omissions to legal responsibility, the Opinion strengthens the normative foundation for transnational claims seeking accountability for climate-related damage, and underscores the importance of due diligence obligations in this field.

What comes next?

The Advisory Opinion delivered by the International Court of Justice on 23 July 2025 offers a carefully structured legal framework for assessing state obligations in the face of the climate crisis. Drawing on principles from customary international law, human rights norms, and the interpretation of treaty commitments, the Court distills several core duties that shape the contours of climate responsibility. Among these are the obligation to prevent environmental harm through rigorous and anticipatory due diligence (para. 149); the responsibility to regulate corporate activity as an integral component of that duty (para. 428); the requirement to pursue the highest possible ambition in climate planning and mitigation (para. 166); and the recognition that affected states may invoke international responsibility in relation to climate-related loss and damage (para. 195).

When taken together, these findings do more than restate existing legal doctrine—they clarify that failure to act in the face of known climate risks may constitute a breach of international law. Crucially, the Court moves beyond abstract commitments to underline the operational dimensions of these duties, emphasizing that climate governance is no longer the exclusive domain of political discretion.

For the field of business and human rights, this carries clear implications: corporate conduct, and the regulatory measures that shape it, can no longer be treated as secondary to global climate accountability. States must take active steps to ensure that companies adopt credible transition pathways. Where they fail to do so, legal consequences may follow—not only in principle, but in practice.

Of particular interest is the the role that litigation will have in the near future, particularly in relation to loss and damage, with necessary reforms to domestic legal and regulatory frameworks.

What the Court has underscored is that the international legal order is no longer silent on matters of climate justice. That silence has been replaced by a clear set of obligations—substantive, procedural, and interpretive—that demand urgent and sustained attention from both public and private actors.